Test devices of this kind are used for checking electronic board assemblies of the most diverse type. Board assemblies of this kind may, for example, be circuit boards, either with or without components, or, for example, highly integrated circuits, of which a plurality are disposed on a wafer, for IC manufacture. The probes may also be of the most diverse kind, for example electric contact points adapted to be connected via relay banks to stimulus sources or measuring amplifiers of a suitable electronic measuring device, or other probes used for other test methods, such as, for example, inductive or capacitive sensors or optical scanners, e.g. cameras or microscopes.
For the rapid testing of relatively large board assemblies, such as, for example, computer motherboards, a plurality of probes are usually provided, which can be positioned independently of one another. A plurality of probes are frequently also necessary so that when a plurality of electric junction points are to be contacted simultaneously it may be possible, for example, to apply a voltage to two junction points and tap off a voltage at a third junction point. Control of the probes is usually effected by means of sequence programs compiled individually for a specific board assembly.
Known test devices of this type are always so constructed that all the probes can be positioned over the total area of the maximum board assembly which can still be tested on the test device. In the conventional construction, the probes are disposed on slides which are adapted to move over the surface of the board assembly by means of spindles in the X-direction and the Y-direction. In the case of raisable and lowerable contact points, vertical drives operating in the Z-direction are provided on the slides.
In the known test devices, the slide guides and drives have to be movable over the entire length of the board assembly for testing, i.e. over considerable lengths which, in the case of a typical PC circuit board, amount to 30.times.40 cm for example. With these considerable traversing distances high spatial resolutions are required. For example, the individual contact pins of modern ICs must be controlled with a length resolution of much less than 1/10 mm. Consequently, extremely stable and heavy mountings and drives are required for the slides, resulting in high moving masses.
A disadvantage of such test devices is the low speed of travel from one point to another, due to the high moving masses. High masses have to be continually accelerated and stopped. Decay times also have to be taken into account.
In modern production lines, for example for electronic equipment, board assemblies are, however, produced at a speed such that known test devices of the type according to the preamble are too slow. Consequently, only individual selected board assemblies can be tested, or else a plurality of test devices have to be used in parallel.
In contrast, test devices having a separate probe for each grid point of the board assembly, i.e. those operating with stationary probes and which do not have the above-mentioned speed problems, have advantages in terms of speed. These test devices, however, are disadvantageous in terms of circuitry and cost, and particularly in respect of the fixed arrangement of the items under test. They are therefore suitable only for a specific board assembly manufactured on a large scale, while the test devices with their movable probes, are suitable for rapid changeover to different board assemblies, i.e. for testing small-scale production runs.